The present invention relates to a dielectric member for carrying electrostatic latent image that is produced in ionography, as well as a process for producing the dielectric member.
An image forming method generally referred to as "ionography" is recently practiced as a means of duplication or printing. According to this method, a support drum having a dielectric film is used as a dielectric member for carrying electrostatic latent image and ions are generated by an ion (charged particle) generating means; then, an electrostatic latent image is formed on the surface of the dielectric member under the action of the generated ions and it is made visible by development with a toner; the resulting toner image is transferred to and fixed on a receiving sheet. The dielectric layer of the dielectric member for carrying the latent electrostatic image formed in ionography is a porous anodized aluminum film. Since the porous anodized aluminum film per se has many micropores open in its surface so that the film has poor wear resistance and toner particles come into pores to cause the problem of image deterioration. Under the circumstances, it was proposed that the porous anodized aluminum film be either subjected to an adsorptive treatment with a silane coupling agent, followed by impregnation with an epoxy resin, or directly impregnated with an epoxy resin containing a silane coupling agent (see JP-A-63-294586). (The term "JP-A" herein used means an unexamined published Japanese patent application.) It has been known to close the pores in the porous anodized aluminum film by impregnation with a wax (JP-A-60-50083) or polytetrafluoroethylene (JP-A-61-193157).
It has also been known to use a different dielectric layer than the porous anodized aluminum film and it is made of a mixture of an inorganic powder, a lubricant and a film-forming resin (JP-A-61-144651).
If the porous anodized aluminum film is subjected to an adsorptive treatment with a silane coupling agent, followed by impregnation with an epoxy resin, or if it is directly impregnated with an epoxy resin containing a silane coupling agent, the result is not completely satisfactory in surface hardness; furthermore, the relative dielectric constant of the film is so great (.gtoreq.ca. 7) that a satisfactorily good electrification property cannot be achieved. What is more, the impregnation step must be followed by not only the resin baking step but also the subsequent step of removing the surface resin layer. Thus, the overall process becomes complex, thereby reducing the product yield and the reproducibility of operating characteristics. Impregnating the film with pore-closing materials such as waxes and polytetrafluoroethylene has also caused various problems such as poor electrification property, low surface hardness and poor adhesion to the porous anodized aluminum film serving as the dielectric layer.
The other conventional approach which is characterized by using the mixture composed of an inorganic powder, lubricant and film-forming resin has presented various problems including embrittlement of the dielectric layer on account of the presence of the inorganic powder, increased complexity of the manufacturing process and the resultant decrease in the product yield.